A funny thing happened on the way to the ambush the other day...

Last session a question came up made me feel like I was inside the movie Inception...a Gnomish Trickster was casting an illusion of a light spell being cast on a pebble being tossed into the air, using Phantasmal Force, as part of an ambush. He cast it away from the party, next to a spot where he had been throwing his voice with Ventriloquism. The question was: does the illusionary pebble with an illusionary light spell cast on it, illuminate the party's foes?

The entire table went silent as everyone tried to wrap their heads around this. After a minute or so I cleared my throat and pointed out that I couldn't believe this had never come up before in more than thirty years of play!

Now, I've always found that illusions can be a real bear to deal with in actual play, as players are generally a pretty imaginative lot. I'd like to think I've gotten much better at adjudicating them (read: not letting them break the game), but you still get into these oddball situations every once in a while.

While I'm not looking for any sort of definitive answer on this, I am very interested in other Judges' (or even Players') thoughts on this. Some of the considerations, as I saw them at the time:

Does allowing one spell to too closely duplicate the effects of another go too far (e.g. can I cast an illusionary Light spell on a target's eyes to blind them)?

I don't think this one is such a problem in most cases, including this specific one, as both Phantasmal and Chimerical Force are higher level spells than Light. If a caster wants to burn a slot on that, fine. Plus, the illusion spells already note that they can appear to duplicate other spells.

Does an illusionary object (e.g. a torch) or spell (e.g. Light) project light as a light-source? Does that light extend beyond the area of the illusion spell (e.g. 20' x 20' x 20'), or stop at the boundary?

A fascinating question to me with all sorts of weird implications, depending on the answer. (If it doesn't illuminate the area, presumably the illusion could include an illusionary view of the area being illuminated...how far down the rabbit hole would you like to go?)

If someone disbelieves an illusion, would light "radiated" by the illusion still illuminate the area?

The answer to this obviously depends on the tack one takes when deciding the nature of an illusion; does it/can it radiate light, or is it merely an image/thing that can reflect light?

At any rate, given a little thought, there are a number of others issues that crop up depending on how one adjudicates the situation. Thoughts?

My personal favorite is that an illusionary light reveals what the person seeing it would expect to see.

So if you drop an illusionary light spell in your own home, it helps you navigate. If you drop one in a cave you've never been in before, it fills in what would make sense from the parts you can actually see. If you know an enemy is there, it would illuminate them; if you have no idea, you don't see them.

I would rule that whether illusions would illunminate an area would depend on the spell signature associated with the original spell. If the spell signature of the illusion was light based, then I would allow it. If it was mentally based, then it woul be closer to what Aryxymaraki suggested.

That's why i love spell signatures. One type of magic missile would set things on fire, another would knock light objects off a shelf, depending on the 'special effect' of the spell

Heh, I imagine this is why 2e D&D seperated illusions into "illusions" and "phantasms." Since we're on the topic...

Does an illusion of a mirror reflect light from its surroundings? If the answer is "yes," then that implies that you could use an illusory mirror to see around corners and see things outside of the illusion's area of effect... Which in turn means you could do all sorts of crazy things with light, like use an illusory lens to light fires, see distant real objects through an illusory telescope, or starve a plant of sunlight by shading it with an imaginary wall. On the other hand, if illusions don't reflect light, that means that they should be incredibly easy to spot - because an object in a dungeon that remains dark instead of becoming illuminated when you walk up to it holding a torch must stand out from its surroundings like a sore thumb.

I guess what I'm asking is "what is an illusion?" Is a given illusion a hologram (a thing that emits real light but doesn't reflect it)? An object with real species (sensory properties) but no other physical properties? A mental trick that only exists in the minds of observers? A hologram that doesn't interact with real light, but which emits light as if it was reflecting it? Something else?

For that matter, does an area of magical darkness cast a shadow? Or is it like silence 15', which doesn't allow sounds to pass through it to listners on the other side?

Good point on Illusions and Phantasms; I raised that very fact as we disussed the situation for a few minutes during the game. But yeah, you're bringing up all sorts of interesting conundrums that arise as soon as you think about it using modern scientific knowledge. They're the sorts of things where I tell my players that they can either kindly knock it off, or they can get ready to roll up a new character.

I actually think the Spell Signature idea might have some legs. Though the character in question is known as "The Miser" on account of his reliance on Bargaining proficiency, and all his spells have become associated with coins in some fashion, so I'm not quite sure where to go with that. Might be hilarious if all his illusions looked "cheap" in some fashion...hmmm...

I just realised I never actually answered the questions from your original post. Serves me right for getting distracted by illusory mirrors.

Q: Does allowing one spell to too closely duplicate the effects of another go too far (e.g. can I cast an illusionary Light spell on a target's eyes to blind them)
A: It depends on the spells. In the case of phantasmal force duplicating light? I wouldn't be too concerned. Light is only a first-level spell, after all. Allowing a spell to duplicate a higher-level spell, though? That sounds like the very definition of overpowered-ness. In such a case, I'd allow the illusion of the spell to have the appearance of the real thing, but only a small fraction of the real thing's effect.

Q: Does an illusionary object (e.g. a torch) or spell (e.g. Light) project light as a light-source?
A: I'd usually rule that yes, an illusion of an object that emits light will emit light. Anything else would result in an unconvincing illusion, and every rule about D&D illusions that I've read has implied that the incongruities in an illusion are fairly hard to spot (typically requiring an ability check or saving throw of some kind, if spotting an incongruity is possible at all). I'd also usually rule that an illusory object casts a a shadow and distorts and reflects light the same way a non-illusory object of its type would, because I'd much rather give players a new tool to creatively solve problems with than have to invent new physics for how illusions interact with sunlight. (That said, I'd probably make exceptions for certain spells on a case-by-case basis. Magic is allowed to defy normal physical laws every now and then.)

Q: If someone disbelieves an illusion, would light "radiated" by the illusion still illuminate the area?
A: There's no standard rules for what happens when you "disbelieve an illusion" in ACKS. (In fact, the term "disbelieve" isn't even part of the ACKS core rules, so far as I can tell.) Every illusion spell has its own rules for what happens when someone makes a saving throw against it, so I'd let that be my guide. For example, the only effect of making your saving throw against the phantasmal force spell is that you don't take damage from any illusory attacks; you can still see the illusion created by the spell - and so I'd rule that the light emitted by an illusory light spell continues to be visible throughout the area, even to those who successfully save.

That's how I'd adjudicate all those questions, but most of that is just my personal preference; I'm sure there's a dozen different ways of handling this sort of thing.

Duplicating spells: For me this would be a "kind of" answer, while an illusion could duplicate the way a spell works it is still an illusion. For example an Illusion of a fireball would still look and behave like a fireball (within the parameters of the illusion spell) but it would still be an illusion. A target would only think they took damage from it, but wouldn't actually take damage from it (though it can be amusing to see the reaction of an individual realising it was an illusion after the fact). Thus illusions can "kind of" duplicate other spells.
As a general rule of thumb, I work on the basis that Illusion can only 'duplicate' spells of equal or lower level than themselves.

Can illusions emit light? Of course it can, without light there is no visual illusion (unless it is purely a non-visual sensory). Sure there is more to it than that, and if its done in very dark area I'd likely give those that care if it is an illusion or not a bonus to see that it is one. While others have mentioned, light is a first level spell, so giving that is a bonus. Illusions can be quite limited or broard depending on the imaginations of the player and DM, I always go with the 'rules as fun' or 'rule of cool' for illusions (as much as i dont care for the latter term).
That said I do like Aryxymaraki's novel take on it.

Disbelieving, still radiate light/effect? Yes, for me disbelieving doesn't negate the effect (unless the illusion spell would say so), it just means the disbeliever is aware the effect is an illusion, and will behave acordingly.

I've always treated the Light/Darkness spell as an illusion itself. If you make the spell using the Player's Guide rules (with a little tweaking for range and duration), you get a level 1 spell. So using something like Phantasmal Force, and imitating the Light spell as part of it, is easily possible.

Illusions are awesomely powerful. In fact, an illusion that "does damage" can actually cause someone to pass out for a round, due to the damage done! But, as powerful as they are, they can only affect the minds of the people around them. An illusary mirror could "reflect" light, but in reality it's only shining its own light in the direction the real light would have reflected - the real light continues on. It might look like it can start a campfire by acting as a lens, but in reality, the campfire itself would be an illusion as well. Of course, combine powerful illusions with one or two other spells (firing "arrows" that are actually Magic Missiles, for instance?), and you can make spells for very low cost that seem like much more powerful spells. For instance, a "telepathy" illusion is barely level one - it doesn't let you hear thoughts, but it lets you send your own! Even Ventriloquism can make someone seem Charmed if you've Silenced them first: sure, he's waving his arms around, but he seems to be agreeing with the other guys!

And as for belief/disbelief... some illusions are "real" in the sense that they are "tricks of the light", while others are not, merely "tricks of the mind". Even disbelieving a spell doesn't completely remove it, you can just see the 'trick'.

You bring up another really great point, which is "disbelief," and what happens when someone makes their Save versus Spells against an illusion. Does the illusion disappear? Can they merely see the zippers, so to speak? It's worth noting that you can disbelieve Phantasmal and Chimerical Force, but not Light, Invisibility, or Ventriloquism. These spells are seemingly doing very different things. Which is fine, but a coherent explanation of what's going on needs to account for all of them.

You bring up another really great point, which is "disbelief," and what happens when someone makes their Save versus Spells against an illusion. Does the illusion disappear? Can they merely see the zippers, so to speak? It's worth noting that you can disbelieve Phantasmal and Chimerical Force, but not Light, Invisibility, or Ventriloquism. These spells are seemingly doing very different things. Which is fine, but a coherent explanation of what's going on needs to account for all of them.
-bobloblah

Heh, you remind me of one of the problems with third edition D&D: They had rules for disbelief, but didn't actually define what "disbelieving an illusion" meant in-setting, which made it weirdly hard to narrate and arbitrate when edge cases came up.

Second edition AD&D (and presumably also earlier editions that I'm not familiar with) was much clearer: "Disbelief" consists of noticing a flaw in a phenomenon that gives away the fact that it is an illusion.

First, let's imagine that (visual) illusions create photorealistic 3D images that reflect light - essentially 3D photographs. Just as a photograph of the sun doesn't light up your room, an illusion of the sun doesn't create daylight. This would raise the question of whether an illusion would be identifiable via infravision - it seems like you'd be able to tell it wasn't real. This would also raise the question of how this image could be disbelieved as it's really there in the sense of really reflecting light. You might say "this is an illusion" but you wouldn't be able to see through it, say. And of course it begs the question of how you could be affected by the illusion if it's just an image. A photo of the sun doesn't burn.

Since we know that illusions can deal damage (illusionary damage, but still) and can be disbelieved, then it seems likely this hypothesis is wrong. Illusions are likely working on the psyche directly rather than creating something seen with the eyes. They are hallucinations, not holograms. That would also explain why Masters of Charm tend also to be Masters of Illusion - both are mind-affecting, with the former dominating the will and the latter deceiving it.

That then suggests Aryx's solution to illusory light is the correct one. "If you drop an illusionary light spell in your own home, it helps you navigate. If you drop one in a cave you've never been in before, it fills in what would make sense from the parts you can actually see. If you know an enemy is there, it would illuminate them; if you have no idea, you don't see them."

So what is "disbelief" in this context? I would harken to the sort of illusions that go viral on the internet. "Is the ballet dancer twirling left or twirling right?" Some people say left, some people say right. But when you understand the illusion, you can choose whether to see her as twirling left, twirling right, or just as an animated image. When you disbelieve an illusion successfully, you gain conscious control over how you sense it.

Since invisibility is built as an illusion spell, this actually suggests that when you're invisible, you're still visible, it's just people think they can't see you - similar to the neural effect known as "blindsight" where the brain is receiving sensory imagery but the conscious mind is convinced its blind.

This line of thinking also leads to the implication that mindless creatures are not affected by illusions.

Since invisibility is built as an illusion spell, this actually suggests that when you're invisible, you're still visible, it's just people think they can't see you - similar to the neural effect known as "blindsight" where the brain is receiving sensory imagery but the conscious mind is convinced its blind.

This line of thinking also leads to the implication that mindless creatures are not affected by illusions.

-Alex

I'd been starting to come around to that myself. "Master of Five Magics" (Lyndon Hardy) put me down a road of thinking about the "caster types" being split via function, rather than power source, and his sorcerers were enchantment & illusion specialized. On top of that things like Phantasmal Killer really tip towards the fact that illusion is a mental effect on the target.

Mechanically, it makes me think that the 'cannot disbelieve' multiplier out of Illusion is mispriced (and that there's no "beneficial effect")

I'd think in this case, Invisibility kinda becomes the second tier of Sanctuary - up from 'save to hit caster' to 'save to see caster', and stays at second level. Then the 'cannot believe' version gets a x2 multiplier to put it to 4th level.

I'm not confident that wouldn't kill the utility of the entire category, though.

Another idea might be to gradiate the saving throw based on distance - if you're massmorphing a bunch of conscripts into ogres, it's more easily believed 1000 feet away than it is within charging distance; as spells get higher in level they're going from VGA to HD to 4K, etc. and getting more believable close up.

On Ventriloquism - Theoretically, there'd be no reason to immediately think that a voice (or many other noises) coming from somewhere unexpected is not real. There's not enough evidence, and it'd take an act of will (saving throw?) to not look in that direction, or stop what you were doing at least.

As a real life example, somebody just knocked their shoe against a desk a couple doors down. Happens all the time, I kept typing. Yesterday, a couple of air vents in the ceiling in our little area here blew air, a light wooshing, for the first time ever in my 18 years here. Damn near everybody failed the save on getting up to go wonder at that.

Aside from other uses, the spell effect itself might make more sense as an effect that turns an attentive target into an inattentive target for the round - also making it a form of enchantment.

The Shadowrun RPG always split spells into Physical and Mana. For illusions this means that Physical illusions are actually converting magical energy into physical stimuli, Ie they create light or sound. Mana illusions are mental only, so they trick your brain into constructing sensory images that are not there.

I always saw D&D/ACKS as the physical type. So I’m my mind they are not redirecting light but making new light, so I would say they can make a flame light image that emits. In terms of and illusionary fireball this would mean it would also glow as it would not be a full illusion if it couldn’t.

In terms of damage you don’t need a mind altering effect to trick the brain into reacting to a stimulus. Sensory stimuli has been known to do that anyway. Seeing is believing, and visual stimuli has been known to creature sensation where no physical sensation exists, eg brushing a fake arm sitting next you your arm eventually can create a feeling like your arm is being brushed.

Overall I prefer to keep it simple, but would see mental illusions as a lesser version of the base spell. This is most likely my history with Shadowrun talking :)

That's a good point. If I recall correctly, 3.5E ultimately made the same division with regard to illusions.

One possible way to address this would be to say that illusions that permit disbelief are in the mind of the beholder, while illusions that do not permit disbelief have a phantsmagorical existence of some sort.